To those dedicated warriors hunched over their keyboards or gripping their pens, ready to fire off an angry salvo about the Americanization of British English to their favorite newspaper, television channel or book publisher, linguist Lynne Murphy has a solemn warning: check a good dictionary first.

Or consider her new book, The Prodigal Tongue: The Love-Hate Relationship Between American and British English, which assaults the British obsession of attacking US English with cold, hard facts.

“There is a tendency in Britain to see linguistic things you don’t like as American,” Murphy told the Guardian.

But Murphy, an American who moved to the UK in 2000, demonstrates repeatedly in her book that both countries’ citizens aren’t very good at knowing which words began in which country.

For instance, while “shambles” may have been a British invention, Murphy says it was Americans who first used it to mean “a scene of disorder or devastation”. (It was, however, a British television writer who invented “omnishambles”).

Her book delves past simply clarifying what Americans call a courgette to explain why the two Englishes aren’t more different, how prudishness changes our experiences at the doctor’s office, and what makes grammar classes a political issue in one country but not the other.

It is not just the British who are taken to task. Murphy challenges her birth country’s habit of fawning over silly British words (which are sometimes American. See “poppycock”) or treating the people who use those words as more intelligent and refined because of how their voices sound.

“Nowadays, pride in American English seems to have gone the same way as our pride in being a monarchy-free republic,” Murphy writes. “The American public enthusiastically consumes news about every British royal birth, wedding or death and fetishizes the U in colour as if it hadn’t deserved the drubbing our ancestors gave it.”

She points to how people from the two countries say please and thank you at inverse rates: with the British saying please more and Americans saying thank you more.

“That tells us a story about British politeness culture being more deferent to saying please, and American politeness culture being more interested in not showing deference but showing appreciation,” Murphy says.

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“Because we do tend to assume ‘the way I say things are just the way things get said’. But we say things for particular reasons and you learn a lot about yourself that way.”

Before arriving in the UK, Murphy had worked in South Africa and was already well-versed in the familiar differences between Englishes, such as lift/elevator and biscuit/cookie.

It was the lesser-known linguistic differences, such as how Americans think a frown is something you do with your mouth and the British think is something you do with your eyebrows, that inspired her in 2006 to start a blog: Separated by a Common Language.

And though Murphy is married to a Londoner and has lived in the UK for nearly 20 years, she has yet to identify all the linguistic differences between the two languages. Murphy, a University of Sussex linguistics professor, says she still leaves administrative meetings at work with notes on phrasings unusual to her American-born ears, such as “not worth the candle”, which means worthless. “I learn new things all the time,” she says.